Digital holography (hereinafter also referred to as ‘DH’) which utilizes interference of light is known as conventional art. Digital holography is technology in which an image of a three-dimensional object is reconstructed by use of a computer on the basis of an interference pattern obtained by irradiating the three-dimensional object with light. The interference pattern is formed by interference between (i) object light obtained by irradiating the three-dimensional object with light and (ii) reference light provided from a light source that is used for irradiating the three-dimensional object with light, and the interference pattern is recorded by use of an image sensor such as a CCD or a CMOS. On the basis of the interference pattern recorded, the computer performs diffraction calculation such as the Fresnel transformation, so that a reconstructed image of the three-dimensional object is generated.
Research of digital holography has been conducted mainly in the field of in-line type digital holography. In-line type digital holography has a problem that a reconstructed image is deteriorated because an unnecessary image component such as zeroth-order diffracted light or a conjugate image is included in data recorded by use of a CCD or the like. In order to solve the problem, there has been proposed technology for obtaining a reconstructed image which is free of zeroth-order diffracted light and a conjugate image. This technology is disclosed in Non-patent Literature 1 and Patent Literature 1. There has also been proposed technology called off-axis type digital holography, in which object light and reference light are caused to enter an image sensor so as to have an angle between the object light and the reference light, so that a desired image component and an unnecessary image component are spatially separated from each other.
However, employing the technology disclosed in Non-patent Literature 1 and Patent Literature 1 or off-axis type digital holography still has a problem. That is, since recording of an interference pattern is performed by use of an image sensor, an interference pattern that contains a halation or a blackening is recorded due to an insufficient dynamic range of the image sensor. This prevents a reconstructed image having a high image quality from being obtained.
On the other hand, in the field of an image sensing device such as a digital still camera or a digital movie camera, high dynamic range synthesis is employed as technology for preventing an image containing a halation or a blackening from being recorded. High dynamic range synthesis is technology in which (ii) image parts having no halation or blackening are selected from a plurality of images obtained by recording an image of an identical object a plurality of times with use of respective different photographic exposure values and (ii) the image parts selected are synthesized into a single image. High dynamic range synthesis can reproduce gray scales of parts ranging from a bright part to a dark part within an image from which halation and blackening have been eliminated.